fix typo

bot.go

@@ -1082,7 +1082,7 @@ func botGraphValueDelta(m *tb.Message) {
 	logInfoDebug("botGraphValueDelta : unit set to %s (factor : %f)", unitName, unitFactor)
 
 	for coID, v := range vals {
-		for i := 0; i < len(vals); i++ {
+		for i := 0; i < len(v); i++ {
 			v[i].Y = v[i].Y / unitFactor
 			if math.IsNaN(v[i].Y) {
 				logInfoDebug("botGraphValueDelta : NaN : %d / %f", coID, v[i].X)